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Aneurysmal Subarachnoid Hemorrhage and Global Warming
Gill, R.S., Hambridge, H.L., Schneider, E.B., Hanff, T., Tamargo, R.J. and Nyquist, P. 2012. Falling temperature and colder weather are associated with an increased risk of Aneurysmal Subarachnoid Hemorrhage. World Neurosurgery 79: 136-142.

The authors write that "in the past two decades, several studies reported that meteorologic changes are associated with monthly and seasonal spikes in the incidence of aneurysmal subarachnoid hemorrhage (aSAH)," and they say that "analysis of data from large regional databases in both hemispheres has revealed increased seasonal risk for aSAH in the fall, winter and spring," citing Chyatte et al. (1994), Lejeune et al. (1994), Langmayr et al. (1995), Feigin et al. (2001), Abe et al. (2008) and Beseoglu et al. (2008).

What was done
Seeking to further clarify and refine this seasonal relationship, Gill et al. identified the medical records of 1175 patients at the Johns Hopkins Hospital in Baltimore, Maryland (USA) who were admitted with a radiologically-confirmed diagnosis of aSAH between 1 January 1991 and 1 March 2009, after which they employed Poisson regression "to model the risk of a patient presenting with aSAH based on maximum ambient temperature (MAT), average relative humidity (ARH), and atmospheric pressure, clustering by season of the year to control for the previously reported relationship between season and aSAH presentation."

What was learned
The six scientists determined that both "a one-day decrease in temperature and colder daily temperatures were associated with an increased risk of incident aSAH," and they indicate that "these variables appeared to act synergistically" and were "particularly predominant in the fall, when the transition from warmer to colder temperatures occurred."

What it means
Gill et al. say their study "is the first to report a direct relationship between a temperature decrease and an increased risk of aSAH," and that "it also confirms the observations of several reports of an increased risk of aSAH in cold weather or winter," citing in this regard the studies of Lejeunne et al. (1994), Jakovljevic et al. (1996) and Nyquist et al. (2001). And thus it is that their study implies that with a significant degree of global warming, there would likely be a significant decrease in the incidence of aSAH.

Abe, T., Ohde, S., Ishimatsu, S., Ogata, H., Hasegawa, T., Nakamura, T. and Tokuda, Y. 2008. Effects of meteorological factors on the onset of subarachnoid hemorrhage: a time-series analysis. Journal of Clinical Neuroscience 15: 1005-1010.

Beseoglu, K., Hanggi, D., Stummer, W. and Steiger, H.J. 2008. Dependence of subarachnoid hemorrhage on climate conditions: a systematic meteorological analysis from the Dusseldorf metropolitan area. Neurosurgery 62: 1033-1038.

Chyatte, D., Chen, T.L., Bronstein, K. and Brass, L.M. 1994. Seasonal fluctuation in the incidence of intracranial aneurysm rupture and its relationship to changing climatic conditions. Journal of Neurosurgery 81: 525-530.

Feigin, V.L., Anderson, C.S., Anderson, N.E., Broad, J.B., Pledger, M.J. and Bonita, R. 2001. Is there a temporal pattern to the occurrence of subarachnoid hemorrhage in the southern hemisphere? Pooled data from 3 large, population-based incidence studies in Australasia, 1981 to 1997. Stroke 32: 613-619.

Jakovljevic, D., Salomaa, V., Sivenius, J., Tamminen, M., Sarti, C., Salmi, K., Kaarsalo, E., Narva, V., Immonen-Raiha, P., Torppa, J. and Tuomilehto, J. 1996. Seasonal variation in the occurrence of stroke in a Finnish adult population. The FINMONICA Stroke Register. Finnish Monitoring Trends and Determinants in Cardiovascular Disease. Stroke 27: 1774-1779.

Langmayr, J.J., Obwegeser, A. and Ortler, M. 1995. Seasonal rupture of aneurysms. Journal of Neurosurgery 83: 182-183.

Lejeune, J.P., Vinchon, M., Amouyel, P., Escartin, T., Escartin, D. and Christiaens, J.L. 1994. Association of occurrence of aneurysmal bleeding with meteorology variations in north of France. Stroke 25: 338-341.

Nyquist, P.A., Brown Jr., R.D., Wiebers, D.O., Crowson, C.S. and O'Fallon, W.M. 2001. Circadian and seasonal occurrence of subarachnoid and intracerebral hemorrhage. Neurology 56: 190-193.

Reviewed 31 July 2013